Iron films of nanometer thickness are of interest because of a variety of potential applications in catalysis,1 environmental remediation,2 optics,3 data storage,4 corrosion inhibition,5 as well as their potential relevance in consumer electronics and coatings products. While many processes that render thin iron films functional occur at their surfaces, their interrogation by spectroscopic probes is often limited by the “strong-absorber” problem associated with macroscopically thick samples of iron and its oxides,6,7 especially in situations where one would like to probe the surface from the iron side. While this issue can, in principle, be overcome with the use of iron films that are thin enough so that light fields are readily transmitted through them, nm thin films have not yet been demonstrated to be of high chemical purity. Moreover, the synthesis of corrosion-resistant iron thin films,5 which are considered to be of high purity once an oxide overlayer is formed, requires high-purity iron sources that are expensive and/or difficult to obtain.
Previous methods used to deposit iron thin films from a metallic iron source5,8,9 employ physical vapor deposition (PVD) techniques, including pulsed laser deposition (PLD),8 thermal evaporation under low vacuum conditions,9 magnetron sputtering,10 and electron beam (E-Beam) deposition.5 Laser and E-Beam deposition processes employ light and particle sources that ablate ions from an iron source to a flat substrate under UHV conditions,11 whereas thermal evaporation involves heating a crucible holding the iron source, followed by the deposition of evaporating atoms onto a substrate.12 Of the PVD methods used to prepared thin iron films, magnetron sputtering can provide the highest sputtering rates. The deposition of corrosion-resistant iron films has been thought to require the use of iron sources having a purity of at least 5N (99.999% Fe), which are difficult to obtain5 and handle.5,13 Moreover, because of iron's high boiling point (2862° C.),14 impurities with lower boiling points, such as zinc or alkali elements,15 if present in the iron source, are expected to be enriched in the gas phase during low-temperature PVD processes and to therefore coat the substrate to a disproportionally larger extent when compared to their abundance in the bulk iron source.